1. Technical Field
The present invention relates to the relay system having the relay device for connecting an external device to the communication device through the delay device.
2. Related Art
Conventionally, as an in-vehicle communications system, a communications system using a bus communications channel such as CAN (Controller Area Network) and LIN (Local Interconnect Network) is known. In such a communications system, ECUs (Electronic Control Units) function as nodes, and a communications network with a plurality of ECUs is formed, as shown in a patent reference 1 (Japanese Unexamined Application Publication No. H08-30873).
By the way, an external device is sometimes connected to the above-described communications network on purpose to add new functions. For example, connecting the external device to the communications network and sending rewriting data (reprogramming data) from the external device to the communication network can rewrite programs stored in an ECU (reprogram).
The method, however, might be used for the wrong purpose, e.g. data stored in the in-vehicle ECUs might be altered by an illegitimate external device connected to the communications network.
Therefore, in a case where an external is connected to the communications network, a relay device is provided between the communications network and the external device for determining whether the external device has legitimacy and preventing illegitimate rewrites. The relay device determines whether frames sent from the external device are legitimate, and sends the determined frames to the communications network of the communications system.
If the data on the communications network is obtained and analyzed, the above-described effect of preventing illegalities by the relay device decreases by half.